The present invention relates to a disc cartridge, for installing a disc-like information recording medium into an information recording and reproducing device which is used for recording information onto a disc-like information recording medium and for reproducing information from the disc-like information recording medium, and for keeping the disc-like information recording medium that is out of the information recording and reproducing device.
As a typical disc-like information recording medium, a flexible disc is known well, which is widely used as an information memorizing means for a personal computer and a word processor. Generally speaking, a flexible disc is housed in a plastic cartridge having a metal shutter that can slide for exposing a part of the flexible disc. When the cartridge including the flexible disc is installed into the information recording and reproducing device, this shutter is moved to slide by a shutter opening and closing mechanism disposed in the device.
In recent years, an optical disc and a magneto-optical disc are developed, which has extremely large memory capacity compared with the flexible disc. The optical disc and the magneto-optical disc are also housed in a plastic cartridge in the same manner as the flexible disc, for protecting recorded information, i.e., for preventing the information recording surface of the disc from being scratched or having adhesion of fingerprints.
The thickness of the optical disc or the magneto-optical disc is larger than the flexible disc. In addition, the optical disc or the magneto-optical disc rotates at a very high speed in the cartridge when recording or reproducing information. Furthermore, distortion of the disc surface and an eccentricity of the disc should be considered. For such reasons, sufficient clearance between the disc and the inner surface of the cartridge must be secured. Therefore, the cartridge including the optical disc or the magneto-optical disc is wide and thick compared with the disc itself.
In addition, the cartridge of the optical disc or the magneto-optical disc has a shutter in the same manner as that of the flexible disc. This shutter can be moved to slide on the cartridge so that the information recording and reproducing surface of the disc is exposed. This shutter is different from that of the flexible disc cartridge in that the sliding movement of the shutter is restricted by a lock mechanism provided to the cartridge. Thus, undesired exposure of the information recording and reproducing surface of the disc due to the sliding of the shutter is prevented when the disc cartridge is out of the information recording and reproducing device.
However, this lock mechanism of the cartridge needs tiny components for downsizing and thinning of the cartridge. Therefore, manufacturing of the cartridge requires a skill. In addition, a special mechanism for releasing the lock state of the lock mechanism is required to the information recording and reproducing device in which the cartridge is installed. Thus, cost increase cannot be avoided.